Magnetic studies of SiO2 coated CoFe2O4 nanoparticles

Abstract

Oleic acid capped CoFe2O4 nanoparticles which exhibit a high coercivity of ∼9.47kOe at room temperature were coated with a robust coating of SiO2. We have used chemical synthesis method to obtain SiO2 coated CoFe2O4 nanoparticles with different weight percentages of CoFe2O4 in SiO2 (1.5, 3.1 and 4.8wt.%). The morphological investigation of the coated nanoparticles by transmission electron microscopy shows that the particles are spherical with average size ∼160nm. Infrared spectroscopy reveals that oleic acid capping on the surface of CoFe2O4 nanoparticles is retained after silica coating process. The complete coating of SiO2 on CoFe2O4 nanoparticles is confirmed by X-ray photoelectron spectroscopy as there is no signature of cobalt or iron ions on the surface. Magnetic measurements show that coercivity of SiO2 coated CoFe2O4 particles remains more or less unaffected as in CoFe2O4 nanoparticles at room temperature. In addition, the temperature dependent magnetic measurements show that at 5K the CoFe2O4 and SiO2 coated 1.5wt.% CoFe2O4 samples exhibit a very high value of coercivity (∼20kOe) which is more than twice as compared to room temperature coercivity value (∼9.47kOe). We conclude that silica coating in our study does not significantly affect the coercivity of CoFe2O4 nanoparticles.